1. Field of the Invention
Exemplary aspects of the present invention generally relate to a sheet conveyance device and an image forming apparatus, such as a copier, a facsimile machine, a printer, or a digital multi-functional system including a combination thereof, and more particularly, to a sheet conveyance device including a pair of rollers and an image forming apparatus including the sheet conveyance device.
2. Description of the Background Art
Generally, a sheet conveyance device employed in image forming apparatuses such as a copier, a facsimile machine, a printer, or a digital multi-functional system including a combination thereof includes a pair of rollers that sandwiches a recording medium to convey it to a predetermined position within the apparatus.
Such a pair of rollers consists of a fixed roller, the position of which is fixed, and a movable roller urged by an urging member, for example, a spring or the like, against the fixed roller, so that the movable roller contacts the fixing roller defining a nip therebetween. When a recording medium advances to the nip, the movable roller separates from the fixed roller by an amount corresponding to a thickness of the recording medium being conveyed against an urging force of the urging member, thereby allowing the recording medium to enter the nip.
As the recording medium is conveyed to the nip defined by and between the fixed roller and the movable member, a frictional force between the recording medium and one of the rollers which is a drive roller is transferred to the other roller (the driven roller) due to an urging force of the urging member, thereby rotating the driven roller. Subsequently, as the recording medium exits from the nip, the movable roller returns to the fixed roller side due to the urging force of the urging member, contacting the fixed roller again.
There is a drawback to this configuration in that after the recording medium passes through the nip between the pair of rollers, the movable roller is urged to the fixed roller side due to the urging force of the urging member to form the nip again, striking the fixed roller and thus producing undesirable vibration.
Such vibration shakes an optical writing unit, for example, an exposure device, in the image forming apparatus, and an ink-jet recording head of the image forming apparatus through the sheet conveyance device or a main body of the image forming apparatus, thereby generating striped patterns known as shock jitter in a resulting output image. Unfortunately, such jitter caused by the pair of rollers striking each other defeats the purpose of producing an image of ever higher quality.
To address such a problem, various methods have been proposed to reduce vibration. For example, Japanese Patent. Application Publication No. 2003-146487 (hereinafter “JP-A”) proposes to attach a flywheel to a shaft of a drive roller of a pair of registration rollers, thereby preventing vibration of the registration rollers.
Typically, a drive transmission system that drives a pair of registration rollers includes a drive motor that drives one of the pair of registration rollers, that is, the drive roller, and a gear that transmits the drive force to the drive roller, enabling the registration rollers to rotate. As the drive motor and the gear engage, vibration is generated undesirably. According to JP-2003-146487-A, however, providing a flywheel to the shaft of the drive roller may prevent the registration rollers from vibration.
In this configuration, even when vibration generated in the drive transmission system which transmits the drive force to the drive roller of the registration rollers is transmitted to the drive roller, the flywheel of the drive roller may transfer a resonance frequency of the drive roller, thus preventing sympathetic vibration of the drive roller. As a result, the drive roller is prevented from vibrating, thus preventing transmission and amplification of the vibration of the drive roller to the recording medium. Ultimately, vibration is prevented from leaking out of the image forming apparatus as noise.
Although advantageous, this configuration only reduces vibration caused by the drive motor that drives the pair of registration rollers engaging the gear that transmits the drive force to the drive roller of the registration rollers. Accordingly, vibration generated in the drive transmission system consisting of the drive source and the gear may be prevented from getting transmitted to the recording medium.
In other words, even if the flywheel is attached to one of shafts of the fixed roller and the movable roller, this configuration does not reduce or prevent vibration when the pair of rollers strikes each other as the recording medium exits from the nip between the rollers.
In view of the foregoing, a device that can reduce vibration caused by the pair of rollers striking each other, thus reducing jitter when the recording medium exits therefrom, is required.